1. Field of the Invention
The present invention relates generally to treating waste paper, waste paperboard or the like for use in recycle paper products. More specifically, though not exclusively, this invention relates to a process for preparing recycle paper pulp from difficult to process waste materials, such as paper stock provided with latex or other polymeric coatings, ultraviolet (UV) cured ink coated stock, and adhesive-containing paper products.
2. Background
There is a growing tendency to recycle waste paper as a source of feedstock for the manufacture of paper products. However, it is very difficult to process certain paper products such as polymer or plastic coated paper products. Examples of such products include milk cartons, ice cream containers, glossy papers, coated boards and the like. Older conventional processes are not only expensive but also may be environmentally unfriendly as they can result in additional undesirable waste products that need to be disposed of.
Relatively new technologies have attempted to address some of these problems. For example, in an article by H. Mamers entitled xe2x80x9cThe Siropulperxe2x80x94a new concept in wastepaper recoveryxe2x80x9d (APPITA, vol. 32, No. 2, pp. 124-128, September, 1978), the use of an explosive release digester is described for defibering purposes which may be used in connection with de-inking. The article suggests that hydrodynamic forces of the explosive discharge combine with the chemical effects of a thermal treatment process to release the ink particles from the fibers, reducing the chemical demand of the process. The pressure increase to achieve the required hydrodynamic conditions is effected by injecting pressurized inert gas into a reactor or digester. Although this method appears to have addressed several of the disadvantages of earlier recycle methods, this method still does not produce the product of desired quality, especially as to its appearance, since it produces darker product. Similarly, various other processes have been developed specifically to address environmental and economic concerns in the processing of waste paper products. One such process is generally known as the drum pulping method, which, however, is not very effective as the moisture used in this process can not effectively defiber the waste paper. In addition, the particle sizes of residual contaminants in waste paper furnish produced by this method are generally not acceptable.
Still more recently, a joint development by Wisconsin Tissue Mills and Stake Technology Ltd. was described in a paper entitled xe2x80x9cSteam Explosion Technology and Fiber Recyclingxe2x80x9d presented at a TAPPI conference in March of 1991. The system described in that paper and related literature includes a digesting chamber where high temperature and pressure are maintained throughout the dwell time, following which the treated waste paper materials are discharged into air at atmospheric pressure and room temperature. The paper lists three runs in which the temperature range was 190xc2x0 C. to 203xc2x0 C., the dwell time was four minutes, and the pressure was approximately 400 psi. The process is described as resulting in particle sizes of residual contaminants of from xc2xd to {fraction (1/10)} that of the contaminants in waste paper furnish produced by repulping without steam treatment. A major disadvantage of this method is that relatively high temperature and pressure conditions are needed. Explosive decompression of the drum chamber to discharge the furnish is not very desirable. Furthermore, downstream operations involve several steps to clean the pulp including removing the color bodies and other materials.
It is an object of this invention to further advance the art of recovery of wastepaper and like material and in particular to provide a process for de-inking the waste paper and to remove contaminants from the treated product.
A further object of this invention is to provide a process which not only addresses all of the above-mentioned problems but also provides a method which is economically attractive to use commercially.
A still further object of this invention is to provide a process for the recovery of difficult to process waste papers which are provided with polymeric coatings such as latex coatings or plastic coatings and UV cured ink paper products using moderate temperature and pressure conditions.
Yet still another object of this invention is to provide a process whereby difficult to process inked paper-containing and polymer-containing waste materials with polymeric coatings or components can be readily converted to recyclable pulp by separating the paper from the polymer components such that the ink and other color bodies are trapped in the polymeric waste as it separates and agglomerates from the pulped paper fraction.
The following references are of general interest: U.S. Pat. No. 4,343,679 discloses a process for reclaiming waste paper without deinking which involves pulping waste paper in the presence of soft water; U.S. Pat. No. 4,381,969 discloses a process for the generation of waste paper, which comprises pulping the waste paper with an aqueous alkaline solution; U.S. Pat. No. 5,122,228 discloses a method of treatment of wastepaper at high temperature in the range of 160xc2x0 C. to about 230xc2x0 C. wherein the furnish is treated in a digester with or without added chemicals but in the presence of saturated steam; U.S. Pat. No. 5,262,003 discloses a process of preparing a suspension of papermaking fibers in water for use in the making of paper, which includes the steps of treating a mass of fibrous materials with steam under pressure in two separate vessels; U.S. Pat. No. 5,302,245 discloses a process for the treatment of wastepaper, which provides for removal of both ink particles and non-ink contaminants; U.S. Pat. No. 5,714,040 discloses a method for recovering fiber from printed wastepaper by loading the wastepaper and water into a continuous batch fiber recovery apparatus; U.S. Pat. No. 5,772,847 discloses a method for processing recycling mill sludge into pulp; U.S. Pat. No. 5,795,479 discloses an apparatus and method for waste recycling and conversion in which municipal solid waste is classified as to density as well as size in a perforated inclined trommel; U.S. Pat. No. 5,895,556 discloses a wastepaper treatment process for the recycle and re-use of wastepaper, which involves treating wastepaper in a repulper with a surfactant in the absence of repulper chemicals, such as caustic, silicate, and peroxide; U.S. Pat. No. 5,900,111 discloses a process for sanitizing post-consumer wastepaper fibers for liquid packages and containers, a paper product for food packaging and a liquid food container, wherein the process involves treatment of a slurry of paper fibers from recycle with hydrogen peroxide; and U.S. Pat. No. 5,958,179 discloses a process for increasing pulp whiteness by bleaching printed wastepaper under intense dispersing mechanical treatment.
All of the references described above and hereafter are incorporated herein by reference in their entirety.
It has been found that paper pulp can be readily separated from difficult to process waste materials utilizing an improved waste treatment process. This process produces high quality paper pulp, which is substantially free of polymeric and color body contaminants. Significantly, the process of the present invention involves considerably fewer steps than conventional processes and advantageously generates less downstream waste.
Thus, in accordance with the practice of this invention there is provided a process for recycling waste materials including waste paper and polymeric waste material comprising the following steps: a) in a first step, the waste materials along with suitable amounts of water are introduced into a pressure vessel wherein the pressure vessel is equipped with agitating means providing shear to thoroughly mix the components of the solid wastes; b) a suitable chemical aid is also introduced into the pressure vessel either during, after or before introduction of the waste materials into the pressure vessel, generally, it is advantageous to introduce the chemical aid in the form of a solution in water soon after the waste material is introduced into the reactor inasmuch as the chemical aid facilitates defibering of the paper fraction of the waste materials; c) the waste materials are then agitated in the vessel by way of the agitating means under shear at an elevated temperature and pressure for a sufficient time to accomplish repulping of the moisture absorptive paper fraction, wherein the pressure vessel is rotated and agitation is carried out in such a way that the separation of component fractions by density and size can thereafter be accomplished; and d) in the final step of a process of this invention, the separated waste materials are discharged from the pressure vessel. The pulped paper fraction is usually, through not necessarily, discharged first, and is substantially defibered and substantially free of polymeric contaminants. The polymeric material is agglomerated and is operative to concentrate other contaminants such as color bodies from the materials.
In another aspect of this invention there is provided a process for recovering a paper pulp fraction from paper-containing and polymer-containing waste materials utilizing a preferred mixing vessel. This mixing vessel is of generally cylindrical configuration mounted to be driven in an inclined rotation about its longitudinal axis. There is provided an array of fixed lifting paddles adapted to agitate the paper-containing and plastic-containing waste materials, as well as a helically configured member. Utilizing this mixing vessel, the process of a preferred embodiment comprises the following steps: the paper-containing and polymeric waste material and water are introduced into the vessel through an inlet thereof; either concurrently or after the introduction of waste materials, suitable amounts of chemical aids are also introduced. The vessel is rotated about its longitudinal axis, so as to agitate the waste material. The vessel is also provided with steam to provide thermal energy to the waste material and to raise the pressure inside the vessel to a level above atmospheric pressure. While the temperature and pressure of the vessel are increased, the rotation of the vessel is continued to accomplish repulping of the moisture absorptive paper fraction.
In accordance with still yet another aspect of the present invention, a specific pressure vessel is of generally cylindrical configuration, having rotatably mounted in its interior, a drum of generally cylindrical configuration that is mounted to be driven about its longitudinal axis. The pressure vessel further consists of an inlet end and a closure member therefor. The drum further has an open inlet adjacent to the inlet of the vessel. The interior of the drum being equipped with at least one helically configured baffle and lifting paddles adapted to agitate the paper-containing and polymer-containing waste materials. Utilizing the pressure vessel in this preferred embodiment, the process comprises the following steps: the waste material and water are introduced through the inlet of the vessel into the inlet of the drum; suitable amounts of chemical aids are introduced in order to facilitate deliberation of the paper fraction of the waste material; the closure member is then closed thereby making the vessel pressure tight; the rotation of the drum about its longitudinal axis is commenced, so as to bring about agitation of the waste material in the drum; the drum is then pressurized with steam to elevate the temperature of the waste material in order to facilitate the sterilization of the waste materials in the drum, and to raise the pressure inside the vessel to a level above atmospheric pressure; the rotation of the drum is continued with added thermal energy to accomplish repulping of the moisture absorptive paper fraction; and finally, the treated waste materials are discharged from the drum and the vessel.
In yet another aspect of this invention there is provided a process for preparing a recycle fiber-containing paper product from paper-containing and polymeric waste materials. In this preferred embodiment, the paper pulp formed in accordance with the practice of this invention is further processed in the production of a recycled sheet of paper, tissue or paperboard, and like products.
The feedstock including wastepaper and polymeric waste utilized in accordance with the invention may include coated feedstock provided with latex coatings, fillers and the like. The coatings or polymeric components may include synthetic polymers such as acrylates and vinyl acetates or natural polymers and pastes of starch or organic pastes, as well as natural and synthetic adhesives. The polymeric material may be in the form of a coating, binder or simply be associated with the paper fiber component as in the case of packaging with a paperboard component and plastic film component. The characteristic feature of the feedstock utilized in accordance with the present invention is that the feedstock includes both cellulosic fiber-containing paper and a resinous polymeric component which is agglomerated during the process and operative to segregate other contaminants from the liberated papermaking fiber. As used herein, the term xe2x80x9cpolymericxe2x80x9d includes waxes, as well as high polymers.
In a particularly preferred process, a paper stock with a polymeric coating is introduced into an inclined rotatable drum provided with a plurality of mixing paddles affixed to the interior surface of the drum together with water and an alkaline agent. The drum is thereafter rotated while maintaining the drum interior at elevated temperature and pressure. The mixing paddles are configured to move the material upwardly with respect to the inclination of the drum thereby mechanically refluxing the material against its natural tendency to flow downwardly with gravity during rotation of the drum. The material is thus well mixed and the polymeric material tends to agglomerate or granulate and concentrate other contaminants within the polymeric phase, while the paper fraction of the waste is substantially defibered into recycle pulp. There is thus provided a recycle pulp phase and a polymeric phase which can be discharged from the drum and readily separated.
These and other objects, features and advantages will become more apparent from the description provided below.